Motorola MCPN750A, IH5 manual Serial Port Signal Multiplexing, Interval Timers

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Functional Description

Interval Timers

The PBC has three built-in counters that are equivalent to those found in an 82C54 programmable interval timer. The counters are grouped into one timer unit, Timer 1, in the PBC. Each counter output has a specific function:

❏Counter 0 is associated with interrupt request line IRQ0. It can be used for system timing functions, such as a timer interrupt for a time-of-day function.

❏Counter 1 generates a refresh request signal for ISA memory. This timer is not used in the MCPN750A.

❏Counter 2 provides the tone for the speaker output function on the PBC (this timer output is not used in the MCPN750A).

The interval timers use the OSC clock input as their clock source. The MCPN750A drives the OSC pin with a 14.31818 MHz clock source.

Serial Port Signal Multiplexing

Due to pin limitations of the J3 connector, the MCPN750A multiplexes and de-multiplexes some signals between the MCPN750A board and the TMCPN710 and the TM-PIMC-0001 transition modules. This hardware function is transparent to the software. The block diagram for the signal multiplexing is shown in the following figure:

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